A medium and a reproduction apparatus for it using a laminated hologram ROM (Read Only Memory) in the prior art is explained below.
FIG. 43 is a figure showing a side face (cross section) of a medium 1′, and shows a structure made by laminating a core layer 2′ and a cladding layer 3′ alternately in which a diffraction grating layer 4′ is provided at a boundary between the core layer 2′ and the cladding liver 3′. The diffractive grating layer 4′ has, for example, a bumpy form (a form of alternate lands and grooves) and is recorded or stores information data.
FIG. 44 is a figure showing a side face of a reproduction apparatus 5′ which reproduces data on the medium 1′, and it is composed of an optical head 6′ and a photodetector 7′. The optical head 6′ has a function of emitting incident light 8′ to the requested core layer 2′ of the medium 1′. A reproducing method is described below. Upon emitting the incident light 8′ to the core layer 2′ that is selected or requested, of the medium 1′ by the optical head 6′, the light is diffracted in accordance with the information data (holographic data) recorded or stored by the diffractive grating layer 4′ and a reproduction light 9′ goes out from a top surface of the medium 1′.
By detecting this with the photodetector 7′, it is possible to reproduce the information data recorded or stored on the medium 1′.
The medium 1 can be small and can have a large storage area, and the reproduction apparatus 5′ can be small because it has a simple structure and construction. The laminated hologram ROM is expected to be small size memory for content distribution with a large capacity. Moreover, by applying the medium 1′ above as an authentication (authorization, certification or guarantee) sheet, it is possible to make the authentication sheet small and having a large capacity, and the reproduction apparatus 5′ can be small because it has a simple structure and construction (see Japanese Patent Application, First Publication No. 2002-19338). This technology is expected to be applied to a authentication sheet such as memory, keys, seals for guarantees, a sticker for packaging, tags, and the like that record a specific identification number.
On the other hand, in recent years, in order to protect the copyrighted contents from illegal copying, counterfeiting and the like, there is a need to append an identification (hereinafter, ID) to a medium of ROM type. In order to satisfy such a need, it is required to record different information data on each medium, and moreover, to reproduce the information data with a reproduction apparatus if possible.
However, in the prior art described above, the medium 1′ is, for example, manufactured in accordance with a stamping technique using an original print, and therefore, it is appropriate to the manufacture of many mediums having the same information data, but it is not suitable to the production of mediums having different information data because in this case productivity and cost do not go together favorably.
Moreover, the medium 1′ is a medium only for ROM, and therefore, it is impossible to write the information data after producing the medium. As explained above, in the prior art, there is a problem that it is impossible to record different information data onto each medium.
Moreover, in the field of applying the authentication sheet above, by storing unique information data on each authentication sheet, it is made possible for each authentication sheet to be authenticated independently, therefore, and there is an advantage in that the application range and fields are expanded.
However, the authentication sheet of the prior art above is produced in accordance with, for example, the stamping technique using the original print the same as the ROM medium above, and therefore, it is appropriate to the production of the authentication sheets storing completely the same information data.
On the other hand, it is not suitable to the production of authentication sheets having different information data because in this case productivity and cost do not go together favorably. Accordingly, in the prior art, there is a problem in that it is impossible to record different information data on each authentication sheet easily.
The present invention is proposed in order to solve the problems above, and an objective thereof is to provide a laminated holographic medium to which data can be recorded, a recording apparatus and method, a reproduction apparatus/method, and a design method of the laminated holographic medium which enable the recording of information data such as an ID even after production of the medium, and which enables reproduction of the ID using a reproduction apparatus for a ROM medium.